1. Field of the Invention
The present invention relates to an in-building repeater, and more particularly, to a process and a multi-sector in-building repeater, capable of maximizing transmission efficiency of by increasing frequency and sector.
2. Description of the Related Art
A widely spread personal communication system (PCS) is the general term for a next generation of mobile communication with client-centered service, which is intended to overcome defective service by mobile phones in a related art; in other words, PCS should provide an ideal communication service through which a person can talk over the phone with others anytime, anywhere, using an easy to carry terminal within an ultra-small and ultra-light appliance.
To implement principles of the personal communication system, it is necessary to allow a user wireless access while moving freely. In addition, a network service provider should help subscribers to make access more easily and provide customer-tailored service for new subscribers by building an intelligent network, whereby an originator and receiver, wherever they are, can have a conversation over the system.
The personal communication system provides a low-price pedestrian-centered mobile communication service. More specifically, its phone charge is relative to cheaper other mobile phones, users can hand-off communications while moving less than 20 km/hr, speech quality equivalent to wired phones is provided, and the mobile station of the system is easy to carry, cheap, ultra-small, and ultra-light.
Moreover, a base station for the personal communication system is usually a small, light micro-cell or pico-cell, and thus, can be easily installed in any place, freely making incoming/outgoing calls and accommodating many subscribers. Since the base station is designed. to be very light and small, it can be set up in outdoor facilities like a utility pole or phone booth, minimizing an amount invested in installation.
In recent years, many personal communication service providers have introduced an in-building repeater for buildings in an urban area. Examples of prior art repeaters are set forth in the following reference incorporated by reference herein: U.S. Pat. No. 5,946,622 to Nils Johan Bojeryd entitled METHOD AND APPARATUS FOR PROVIDING CELLULAR TELEPHONE SERVICE TO A MACRO-CELL AND PICO-CELL WITHIN A BUILDING USING SHARED EQUIPMENT describes an apparatus and method for providing cellular telephone service to a pico-cell located within a building and extending cellular telephone service from a macro-cell located outside the building to a receiver inside the building; U.S. Pat. No. 6,374,119 to Ju-Sung Jun et al. entitled SYSTEM AND METHOD FOR IN-BUILDING MOBILE COMMUNICATIONS describes a system and method for mobile communications which remove blanket areas of communications using a mobile repeater.; and U.S. Pat. No. 6,501,942 to Haim Weissman et al. entitled IN-BUILDING RADIO-FREQUENCY COVERAGE describes a repeater apparatus for conveying a radio-frequency (RF) signal into an environment closed-off to the RF signal, including a master transceiver unit and one or more slave transceiver units, each unit positioned within the environment closed-off to the RF signal.
The following describes an in-building repeater of a related art, using CDMA (Code Division Multiple Access) mobile communication system as an example.
The in-building repeater as typical practiced in the related art may include such elements as antennas, duplexers, low noise amplifiers, preamplifiers, intermediate-frequency modules, surface acoustic wave (SAW) filters, mixers, and a power amplifier.
Operating principles of the in-building repeater are now explained below.
When a high frequency signal is received from a base station through, for example, through a Yagi antenna, the received signal is transmitted to a low noise amplifier in the transmission direction through a duplexer. Then the low noise amplifier and a preamplifier amplify the signal, and a intermediate-frequency (IF) module converts the amplified signal into an intermediate frequency signal. Next, a SAW filter removes noise from the signal that is output from the IF module, and a mixer converts the noise-free signal into a high frequency signal. The converted signal is amplified in a power amplifier, passed through another duplexer, and is then radiated through an in-building antenna.
On the other hand, a high frequency signal transmitted from a mobile station of a subscriber is received through the in-building antenna, passes through a duplexer, and is amplified by the low noise amplifier and preamplifier. This high frequency signal, having been amplified by the preamplifier, is converted into an IF signal in the IF module, and noise in the amplified is removed by the SAW filter. The noise-free signal is then converted into a high frequency signal through the mixer. The converted high frequency signal is amplified by the power amplifier, passed through another duplexer, and then is radiated from the Yagi antenna to be transmitted to the base station.
The in-building repeater using the Yagi antenna of the related art can be used however, only on a single floor or in a particular space in a building. To radiate the frequency wave to other floors, a leaky coaxial cable(LCX) is utilized, in an attempt to radiate the wave to every spot in the building.
Recently, according to related efforts in the art, an in-building repeater was installed in several floors of a building. When providing personal communication service to a mobile station, a high frequency wave (1.8 GHZ) is received through an Yagi antenna external to the in-building repeater, and the high frequency signal is then converted by a digital unit into a low frequency wave. Next, a distributor distributes the low frequency signal, and a remote access unit (RAU) in each service layer of the in-building repeater converts the distributed signal back to a PCS frequency, namely 1.8 GHZ, to make it appropriate for communication service.
The high frequency signal is not transmitted directly from the digital unit to the remote access unit, but is first converted into a low frequency wave at the digital unit before transmission, because when high frequency signals are transmitted between the digital unit and the remote access unit via wire, transmission loss often occurs and transmission of signals to a distant place becomes very difficult.
As such, a circuit for radiating low frequency signals between the digital unit and the remote access unit is called a repeater, and depending which type of medium is used between the digital unit and the remote access unit, the repeater selected maybe one of several kinds: RF(Radio Frequency) repeater used is only for amplifying signals without converting the signals, an optical dispersion repeater which uses optics, a micro repeater which uses microwaves, and a converting wave repeater which acts as a frequency converting repeater; usually, one of the first three types of repeater is used.
The structure of an in-building repeater using an light dispersion antenna may include duplexers, low noise amplifiers, mixers, filters, optical transmitters, optical receivers, an light dispersion antenna, and power amplifiers.
The operation of a repeater using a light dispersion antenna is similar to that of the previously described repeater, except that the high frequency signals in this system are converted into optical signals which are transmitted through optic cables and the optic signals are radiated to blanket the intended areas of reception through the light dispersion antenna.
Probably the most ideal cell design when the radio efficiency of the in-building repeater is taken into consideration, is an 1 FA (Frequency Assignment) Omni system, although an appropriate scheme for handover between public networks should be plotted out, this will not be discussed here because this scheme may be implemented by many alternative plans.
If there are so many service subscribers in the same building and thus, a number of sub-cells are needed, basically there could be two methods: one is to extend FAs and the other to increase sectors.
For instance, suppose that there is a twelve-story building. If the former method of extending FA is applied, a 12 FA omni service should be provided, and if the latter method of increasing sectors is applied, six sectors may be assigned for each FA by taking two floors of the building as one unit cell.
When extending FA, the number of repeaters at the far-end may be increased. Generally, the number of repeaters at the far-end is limited by the total output power. If a maximum of 10 mW is provided to one frequency, and there are a total of 12 frequency assignments, output of each FA is limited to between one and two mega-Watts. This means that many repeaters should be installed in the same space.
Another defect in the approach of extending FAs is that if a building is located in proximity to a public network service, the frequency being used is usually the same, raising the possibility that handover or disconnection will frequently occur.
When using the approach of increasing sectors, on the other hand, the sector structure at a base transceiver station (BTS) is basically more complex than the omni structure, its implementation involves great costs, and transmission loss is likely to happen because of interlayer handover.
Moreover, when an IF repeater is used, it is not simple to merge signals for six sectors. and transmit to each floor because the signal will be the same FA. Thus the signals have to be provided to each floor through different paths, respectively.